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Pathogenesis, Clinical Features and Diagnosis

Presentation of uncomplicated influenza

The clinical presentation of influenza ranges from an asymptomatic infection or a self-limiting upper respiratory tract infection (URTI) to a severe illness, often with serious, potentially fatal, complications. 12 x TR Cate. Clinical manifestations and consequences of influenza. Am J Med 82 (1987) (15 - 19) Crossref. The incubation period is 1–4 days, with an average of 2 days. The clinical course is dependent on the virulence of the virus. The age of the patient (the very young and the old), and the presence of chronic medical illness, such as cardiac and pulmonary diseases, immunosuppression and pregnancy enhance the severity of illness.

The typical uncomplicated influenza A syndrome is a symptom complex that overlaps with a number of other respiratory illnesses. There is an abrupt onset, with high-grade fever (38–40°C) being the most prominent symptom. Other symptoms include headache, chills, dry cough, myalgia, malaise and anorexia. In more extreme cases, severe malaise with prostration is observed. Respiratory symptoms such as rhinorrhoea, nasal congestion and sore throat are present, but are overshadowed by the systemic symptoms during the first 3 days of illness. The influenza virus tends to remain in the respiratory tract and does not usually cause a viraemia. Systemic symptoms are due to proinflammatory cytokines, which are released following activation of the host's defence mechanisms (see Chapter 4). The cough frequently changes from a dry, hacking nature to one that is productive of small amounts of sputum that are usually mucoid but can be purulent. After the fever and upper respiratory tract symptoms resolve (usually within 7–10 days), cough and weakness can persist for 1–2 additional weeks. The frequency of influenza symptoms in adults, shown in Figure 21 , may vary with the age of the patient.

Figure 21 Influenza symptoms and their associated frequencies. source: Data are from 10 studies involving 520 adults with uncomplicated influenza A. Adapted from Nicholson KG. Human influenza. In: Nicholson KG, Webster RG, Hay AJ, editors. Textbook of Influenza. Oxford: Blackwell Science, 1998; pp. 219–264 with permission from Blackwell Publishing.

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  • The frequency of influenza symptoms in adults, shown in Figure 21, may vary with the age of the patient.
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x

Figure 21 Influenza symptoms and their associated frequencies. source: Data are from 10 studies involving 520 adults with uncomplicated influenza A. Adapted from Nicholson KG. Human influenza. In: Nicholson KG, Webster RG, Hay AJ, editors. Textbook of Influenza. Oxford: Blackwell Science, 1998; pp. 219–264 with permission from Blackwell Publishing.

f05-21-9780723434337

References in context

  • The frequency of influenza symptoms in adults, shown in Figure 21, may vary with the age of the patient.
    Go to context

References

Label Authors Title Source Year
12

References in context

  • The clinical presentation of influenza ranges from an asymptomatic infection or a self-limiting upper respiratory tract infection (URTI) to a severe illness, often with serious, potentially fatal, complications.12 The incubation period is 1–4 days, with an average of 2 days.
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  • In otherwise healthy individuals, influenza infection normally results in an uncomplicated URTI that resolves within 1–2 weeks.
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TR Cate. Clinical manifestations and consequences of influenza. Crossref. Am J Med 82 (1987) (15 - 19) 1987

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